In modern mobile telecommunication systems employing high data rate communication schemes, communication resources are dynamically allocated, or scheduled, to mobile stations on the basis of channel qualities and interference conditions experienced by the mobile stations. A given mobile station estimates the quality of given transmission resources, such as frequency sub-bands, and transmits the quality of the transmission resources to a serving base station for scheduling.
Additionally, it is anticipated that mobile telecommunication stations will support multiple spatially parallel transmission streams between the base station and the mobile station, wherein independent data is transmitted in the parallel transmission streams in order to provide higher data rates. For such a purpose, the mobile stations are equipped with a plurality of antennas.
For efficient utilization of available communication resources, mobile stations may also determine the number of independent (or sufficiently uncorrelated), spatially parallel communication streams and transmit also this information to the base station. The mobile station may calculate the quality of a given transmission resource and the number of independent spatially parallel communication streams in that transmission resource from a pilot signal transmitted on the transmission resource. The mobile station may calculate from the received pilot signal a channel matrix representation representing properties of a radio channel between antenna arrays of the base station and the mobile station. In more detail, the channel matrix representation may be calculated from a channel response matrix including elements indicating the response of the radio channel between any two transmitter-receiver-antenna pair. The number of independent spatially parallel communication streams is determined by calculating a rank of the channel matrix representation. In theory, the rank of a matrix is defined as the number of non-zero eigenvalues of the matrix. In this context, however, a rank is defined as the number of eigenvalues of the matrix differing sufficiently from zero. The number of the independent, spatially parallel communication streams is proportional to the number of eigenvalues of the matrix differing sufficiently from zero. The sufficient difference may be determined with a threshold.
The calculation of the rank is, however, a computationally complex procedure. Iterative methods have been proposed for calculating the rank, but the expected complexity of these methods is unknown beforehand and, thus, they are not ideal for use in mobile stations with limited computational resources. Another solution for calculating the rank is through solving roots of a characteristic equation of the matrix. However, this includes calculation of a square root which is a complex operation from a implementational point of view. Accordingly, a need exists for reducing computational complexity of the rank estimation procedure.